This invention relates to an attachment for a numerically controlled turret lathe to enable the bar stock workpiece to be displaced in the spindle chuck or collet. Such displacement is desired, for example, in multiple piece work where workpieces are machined and severed from an elongated supply stock and it is desired to automatically reset the supply stock in the spindle chuck for machining of the next piece. Conventionally, this stock reset is accomplished either by hand or by an auxilliary stock feed device mounted behind the spindle chuck for hydraulically controlled incremental transport of the stock material through the chuck to the work area. In addition to the expense of the device, the internal electronic transport control of the feed device must be coordinated with the master operation controls of the numerically controlled lathe. Additionally, as the feed mechanism is operated from behind the chuck, the complete length of the bar stock cannot be fed through the chuck which results in stock waste.
Front mounted stock pullers have been proposed but have not heretofore been operationally successful. For example, one device designed for turret mounting utilizes a tapered sleeve to engage the outer periphery of the workpiece and pull the piece a predefined displacement after a press fit engagement. The number of different sized sleeves required to accomodate different sized workpieces makes the device inconvenient to use. Furthermore, because the tapered press grip accentuates diameter differences in the finished or unfinished bar stock, the sleeve may not consistently locate itself with relation to the stock during engagement, resulting in variations in successive stock displacements or complex error adjustment routines in the control system.
In a numerically controlled turret lathe the turret position and displacement, and the chuck opening and closure can be controlled by appropriate preprogramming of the lathe. It is therefore desirable to utilize the turret for installation of a bar puller as electronic instructions and dynamic action to effect the bar pull operation can be largely accomplished by the internal controls of the lathe system itself. The automatic bar puller of this invention is designed for installation on one of the turret stations of a numerically controlled turret lathe, and is entirely mechanical in operation relying on the control system of the turret lathe to initiate the sequential actions that trigger the actuation of the puller.